Hitherto, as a method of forming a penetrating structure section on a circuit substrate, the following method is used. That is, a section to be formed a penetrating structure in a circuit of a circuit substrate which has been thinned to have a thickness equal to the thickness of a final product in advance, is melted and removed by a laser beam or plasma irradiation, to form the penetrating section. The method of manufacturing the circuit having the penetrating section is an extension of a method of manufacturing a semiconductor wafer, and the circuit is formed on a wafer made of silicon and the like.
Examples of applications or usage of the circuit substrate having such a penetrating structure include, for example, various motion sensors each having an MEMS (micro electromechanical system) structure section.
As these circuit substrates, in general, a silicon or compound semiconductor wafer, or a substrate made of various glasses or ceramics, are used. Of these wafers and substrates, a silicon wafer, which is widely used, is manufactured such that a high-purity silicon ingot obtained by a single-crystal pulling method is sliced into wafers each having a thickness of about 500 to 1,000 μm. A penetrating structure is formed in a surface of the silicon wafer manufactured as described above, by the similar manufacturing method as a method of forming a circuit pattern on a semiconductor wafer, thereby to manufacture various motion sensor circuits. Then, to thin the wafer in which the penetrating structure is formed to have a predetermined thickness which is adapted to various applications or which is required for the characteristics of various motion sensors, the backing surface of the waver is subjected to grinding by a device, which is called a back-side grinder, to obtain a thinned film. Further, if necessary, a stress relief processing typified by chemical etching, CMP (chemical mechanical polishing) or the like, may be performed, to remove grinding distortion such as a crushed layer resulting by grinding.
Thereafter, a section to be formed the penetrating structure in the circuit is processed by partial cutting by a laser beam or plasma irradiation, to form the penetrating structure by penetrating the wafer, thereby manufacturing a circuit substrate. Meanwhile, recently, it is studied that a wafer itself is further thinned, in order to attain improvement in the performance of a motion sensor.
In the meantime, in the conventional method of manufacturing a circuit substrate having an MEMS structure section, when a predetermined wafer thickness at the time the MEMS structure section is formed is so large as 300 μm or more, the wafer itself is not broken by grinding of the wafer, and the wafer itself is high in mechanical strength. Therefore, in handling of the wafer when the MEMS section is formed in the wafer after being subjected to the grinding, the wafer and/or the MEMS structure section is hardly broken or cracked. Accordingly, such a thick circuit substrate can be stably manufactured, without any problem in a yield in manufacture thereof.
On the other hand, in recent years, with increasing use of a semiconductor, such as mounting on a mobile device, a three-dimensional high-density mounting-type package, as typified by a stacking-type CSP (chip size package), has been rapidly and widely spread. According to this, with equalization of a chip area and a package projection area and decreasing to make a package thickness thin, a chip itself to be mounted must be thinned, i.e. the thickness of a semiconductor wafer itself must be extremely decreased to be 25 to 100 μm. Similarly, even in various motion sensors, with further improvement of performance and the like, the circuit substrate is further thinned. In various motion sensors, it is not required at the current state, to extremely thin those, contrary to that in the above semiconductor cases. However, when the predetermined thickness of a circuit substrate such as a wafer is small, i.e. 300 μm or less, or about 100 μm which is frequently examined currently, the following problem occurs. That is, a defect, such as breakage or crack, is apt to be caused by inter-step conveyance or contact between the wafer and a jig or the like, when a penetrating structure section is formed in the wafer after grinding, thereby a yield of products conspicuously decreases.
Further, the following method is also known. That is, while a tape material adheres to a surface of the wafer on which the circuit is formed, the backing surface of the wafer is ground and etched, and then a region corresponding to a semiconductor device is masked, and the wafer is etched from the backing surface side, to separate the wafer into individual semiconductor devices. However, this method is not a method of manufacturing a circuit substrate having a penetrating structure.